couchdb

A document database server, accessible via a RESTful JSON API

Apache CouchDB is a document-oriented database that can be queried and indexed
in a MapReduce fashion using JavaScript. CouchDB also offers incremental
replication with bi-directional conflict detection and resolution.

CouchDB provides a RESTful JSON API than can be accessed from any environment
that allows HTTP requests. There are myriad third-party client libraries that
make this even easier from your programming language of choice. CouchDB’s built
in Web administration console speaks directly to the database using HTTP
requests issued from your browser.